Temperature and humidity dependence on aerosol composition in the northern Kyushu, Japan

Aerosol samples were collected continuously from October 1990 to February 1992 at a rural site in the northern Kyushu and characteristics of aerosol composition are investigated. The seasonal variation of particulate SO42− concentration is not significant, but it decreased during the rainy sampling conditions. On the other hand, particulate NO3− and Cl− concentrations decreased in summer. The hourly and seasonal variations of NO3− are related to a photochemical reaction and gas/particle equivalent for nitrate. Under the conditions of high atmospheric temperature the dissociation of particulate NH4NO3 to its precursor HNO3 and NH3 is enhanced and dissociated HNO3 is readily removed from the atmosphere through the surface deposition process. Gaseous nitric concentration (HNO3) is estimated from the data of particulate NH4+, NO3−, SO42− Na+, Cl− and ambient temperature. The estimated HNO3 concentration is well correlated with the ambient temperature having the regression function of ln(HNO3)2 = 68.3 − 20,100/T. This relationship coincides with the theoretical equation for the dissociation equilibrium of NH4NO3.